The present invention relates to a power transmission device for a motor vehicle and, more particularly, to a power transmission device for a four-wheel drive vehicle.
A majority of the passenger vehicles manufactured today are front wheel drive vehicles. These vehicles use a transaxle assembly to distribute the power from the engine to the front drive wheels. The transaxle assembly is a combination of a transmission and a front differential packaged together as a single unit. This transaxle assembly is connected directly to the engine.
Due to the increasing popularity of four-wheel drive vehicles, the need was created for a power transmission device which would convert a front wheel drive vehicle into a four-wheel drive vehicle. Various devices are now available which incorporate a power take-off unit into a transaxle assembly for providing power to the rear wheels of a front wheel drive vehicle, thus making the vehicle four-wheel drive.
While these devices have enjoyed various amounts of success, they all have the common problem of limited availability of lower gear ratios. A large majority of the transaxles in volume production are designed for passenger car or on-road usage. The transmission ratios and final drive ratios available in these transaxles were developed for highway driving. The transaxle cases manufactured for front wheel drive vehicles do not provide sufficient room to accommodate the larger diameter gears which are needed to produce the lower gear ratios desired by the sport and light truck market. The sport and light truck owners take their vehicles "off road". They, therefore, desire a lower gear ratio to enable them to maneuver their vehicles through typical off road conditions. The tooling costs associated with providing a unique transaxle for a four-wheel drive version of a vehicle is prohibitive.
Accordingly, what is needed is a power transmission device for four-wheel drive vehicles which utilizes the gear ratios available in current production front wheel drive vehicles but still provides the lower gear ratios desired for the off-road drivers.